Workers feel unable to disclose mental health problems to colleagues or bosses because discrimination is rife and openness discouraged, according to research to be published tomorrow. As many as one in four workers have experienced discrimination or witnessed colleagues being discriminated against at work because they suffered from a mental health problem, according to a new survey by the charity Mind.

Experts say good communication in the workplace is essential if people are to open up about problems before spiralling into depression and anxiety.

Mental illness is the most common health problem to affect people of working age: one in six suffer from severe stress, depression or addiction at any one time. The financial effects alone are startling, with a cost to UK businesses of more than £26bn last year, according to the Centre for Mental Health (CMH).

Mind is campaigning to challenge stigma, bullying and inadequate support services. It wants to persuade employers that spotting staff struggling with stress and mental health problems and then providing the right support will save them billions in sick leave and poor productivity.

One in four workers said their bosses rarely or never asked them how they were. Less than half said their bosses regularly listened to their viewpoint, while two-thirds said they do not feel valued at work.

Amy Whitelock of Mind said: "Mental health problems remain the elephant in the room. Poor communication fuels the problem because if your boss or manager doesn't even ask how you are, how could you possibly approach them about anything more sensitive? There is still a culture of denial which means employees are afraid to speak out because they fear discrimination or being thought of as weak, and employers are afraid to broach the subject in case they make things worse."

Fear of being bullied or isolated means workers are more comfortable taking time off for physical ailments than depression or anxiety, according to Mind's survey of 2,006 people. This means thousands go to work every day despite feeling mentally under par, costing the economy £16bn a year in underperformance or "presenteeism", according to the CMH. Its new report, Managing Presenteeism, to be launched later this month, will show employers how to reduce the burden through early detection and better support for mental health problems.

Andy Bell, chief executive of the CMH, said: "The openness message must come from the top, but line managers and supervisors are key, as they are the ones who will first notice if someone isn't performing. Disclosure is incredibly difficult but the onus is clearly with the employers, and the business case is clear."

Case Study: Pippa, 32, high street bank cashier

Pippa (not her real name) has suffered from bouts of depression since the age of 17

"I didn't tell the bank about my depression in my job application because I knew they wouldn't give me the job. In my first few months, I did so well that I was awarded the 'rising star', but the expectations are unrealistic and, since being signed off for two weeks in January, I've been passed over for promotions.

"They monitor you to make sure you are smiling all the time, even when you're not with a customer – it makes you feel like a robot. Everyone knows the bank moves problem people to other branches, so I am scared to ask for support. My line manager pointed out how much I'd cost the company by taking time off.

"Officially they encourage you to tell them if you have a problem, but that's not how it works in reality. My manager is so cold, thick-skinned and unapproachable."